Concentration measuring apparatus

ABSTRACT

There are provided a sample cell containing a solution containing an optically active substance between a polarizer and an analyzer of a Nicol system, a first photoelectric detector disposed to receive the light activated in accordance with the concentration of the optically active substance, a second photoelectric detector disposed to receive the light transmitted through the solution independently of the optical activity, and means for determining the ratio of the outputs of the first and second photoelectric detectors. Where the concentration measuring apparatus is used to independently measure the concentrations of pulp and clay in a solution used in a paper making process, said means for determining the ratio of the outputs of the first and second photoelectric detectors determines the concentration of the pulp. In this case, there is further provided a transmission and scattering type concentration meter including a third photoelectric detector for receiving the light transmitted by the pulp and clay, a fourth photoelectric detector for receiving the light scattered by the pulp and clay, second means responsive to the outputs of the third and fourth photoelectric detectors to provide an output corresponding to the concentrations of the pulp and clay and means responsive to the outputs of the first and second means for determining the concentration of the clay.

Unite States Patent 1191 Tamate et al.

1 51 Apr. 3, 1973 1541 CONCENTRATION MEASURING APPARATUS [73] Assignee:Yokogawa Electric Works Limited,

Tokyo, Japan [58] Field of Search ..356/72, 116, 114, 104, 246, 356/206,208, 128; 250/225 [56] References Cited UNITED STATES PATENTS 3,518,0036/1970 Meyn ..356/1l6 3,468,607 9/1969, Sloane et a1. ..356/1162,963,938 12/1960 Irland et a1. ..356/2l2 3 ,027,461 3/1962 Kavanagh..356/ l 04 3,310,680 3/1967 Hasegawa ..356/104 FOREIGN PATENTS ORAPPLICATIONS 386,537 12/1923 Germany ....356/116 5/1959 Switzerland.....

12/1967 Great'Britain ..356/ll6 Primary Examiner-William L. SikesAssistant Examinere-J. Rothenberg Attorney-Chittick, Pfund, Birch,Samuels & Gauthier [57] ABSTRACT There are provided a sample cellcontaining a solution containing an optically active substance between apolarizer and an analyzer of a Nicol system, a first photoelectricdetector disposed to receive the light activated in accordance with theconcentration of the optically active substance, a second photoelectricdetector disposed to receive the light transmitted through the solutionindependently of the optical activity, and means for determining theratio of the outputs of the first and second photoelectric detectors.

Where the concentration measuring apparatus is used to independentlymeasure the concentrations of pulp and clay in a solution used in apaper making process, said means for determining the ratio of theoutputs of the first and second photoelectric detectors determines theconcentration of the pulp. In this case, there is further provided atransmission and scattering type concentration meter including a thirdphotoelectric detector for receiving the light transmitted by the pulpand clay, a fourth photoelectric detector for receiving the lightscattered by the pulp and clay, second means responsive to the outputsof the third and fourth photoelectric detectors to provide an outputcorresponding to the concentrations of the pulp and clay and meansresponsive to the outputs of the first and second means for determiningthe concentration of the clay.

7 Claims, 13 Drawing Figures PATENTEDAPR 3 1m SHEET 1 OF 6 INVENTOR 5TOKUTARO TAMATE HIROKAZU HABUCHI TSUTOMU HIRAYAMA BY Qjlmv mx M 3MWORNEY PATENTEUAPM I973 3.724.957

SHEET 2 BF 6 H n: F IG 5 E A ,q E O H O E ao- I O E-1 Z3 I1=I1 mB his Ed32 52 E 10- C E] 2 Eglfl 2:; IrImNSln (HUB 8 CONCENTRATION OF PULP((9/6) 2 F 16.5 B E U 40- El 53 g 30 11 1m8-[dc m I14 m 20- HA 2 1 1[xiv m on: w

CONCENTRATION OF SUGAR /u) I TOKUTARO TAMATE HIROKAZU HABUCHI TSUTOMUHIRAYAMA BY W?W, M k 6 RNEY INYENTORS v PATENTEUAPR 3 I975 sum 3 or 5 VMHHHE UZHQMOOHM rmO ZOHHOEQRHHQ CONCENTRATION OF PULP (9/4) m B B 4 L 0MHHME UZHQEODHM .mO ZOHHOHQRHHQ CONCENTRATION OF SUGAR W0) INVENTORSTOKUTARO TAMATE HIROKAZU HABUCHI TSUTOMU HIRAYAMA WT? "B 1 ATTORNEYPATENTEDAPR 3 I973 SHEET '4 0F 6 @HHHE GZHHAwUHQZH .mO ZOHH OHQZHCONCENTRATION OF PULP UZHQmOUmZHH r rO rnnu EHHHE 20 H H U HQZH ANGLE}OE ROTATION OF i OLALIZEMDe rees) INVENIOR s TOKUTARO TAMAT-h- HIROKAZUHABUCHI TSUTOMU HIRAYAMA BYg kBwl,

ATTORNEY PMENTEUAPR 3 I976 SHEET 5 [IF 6 INVENTORS TOKUTARO TAMATEHIROBAZU HABUCHI TSUTOMU HIRAYAMA BY WWW, mwom ATTORNEY PATENTEDAPR 3I913 OUTPUT OUTPUT SHEET 8 BF 6 CONCENTRATION FIG.

0- pulp Clay CONCENTRATION INVENTOR S TOKUTARO TAMATE HIROKAZU HABUCHITSUTOMU HIRAYAMA BY TEAL,

SM 37 GA'JLLIFETORNEY CONCENTRATION MEASURING APPARATUS BACKGROUND OFTHE INVENTION This invention relates to a novel concentration measuringapparatus wherein the concentrations of pulp or sugar in solutions aremeasured by utilizing the optical activity of pulp or sugar.

In most of the prior art concentration measuring apparatus of the typedescribed above, a sample cell formed by a pair of parallel transparentglass plates which are disposed with a small gap therebetween isgenerally used,- but with such a cell where a solution of pulp and thelike passed through the cell contains solid contaminants or lumps ofpulp, such solid contaminants or lumps will partially clog the spacebetween the glass plates, that is the cell, thus disturbing the flow ofthe solution in the cell with .the result that accurate measuringbecomes impossible. Further, as the light transmitted through the cellis directly measured, the

measurement is influenced by the scattered light component. In otherwords, the result of measurement is not exactly proportional to theconcentration, thus degrading the linearity of the result.

SUMMARY OF TI-IE INVENTION It is therefore a principal object of thisinvention to provide a novel concentration measuring apparatus ofexcellent characteristic free from the above defects.

Another object of this invention is to provide a novel concentrationmeasuring apparatus having an improved sample cell which is not affectedby solid contaminants or lumps contained in the solution to be measured.

Still another object of this invention is to provide new and improvedconcentration measuring apparatus including means to eliminate scatteredlight components contained in the transmitted light.

A further object of this invention is to provide novel concentrationmeasuring apparatus which can be readily calibrated without thenecessity of using a standard liquid.

A still further object of this invention is to provide an improvedconcentration measuring apparatus capable of independently measuring theconcentrations of pulp and clay contained in a stock inlet or whitewaterin a paper making process. 7

According to this invention, there is provided concentration measuringapparatus comprising an orthogonal Nicol system including a polarizerand an analyzer, a sample cell disposed between the polarizer and theanalyzer and adapted to contain a solution containing an opticallyactive substance, a first photoelectric detector disposed to receive thelight with its polarized plane rotated in accordance with theconcentration of the optically active substance in the solution, asecondphotoelectric detector disposed to receive the light transmittedthrough the solution independently of the optical activity, and meansfor determining the ratio of the outputs of the first and secondphotoelectric detectors.

When the concentration measuring apparatus just described is used toindependently measure the concentrations of pulp and clay contained in asolution used in a paper making process, the solution is passed throughthe sample cell. Then the means for determining the ratio of the outputsof the first and second photoelectric detectors determines theconcentration of the pulp. In this case, according to this invention,there is further provided a transmission and scattering typeconcentration meter including a lens for transmitting parallel lightthrough the solution in the sample cell, a third photoelectric detectordisposed to receive the light transmitted by the pulp and clay, a fourthphotoelectric detector disposed to receive the light scattered by thepulp and clay, second means responsive to the outputs of the third andfourth photoelectric detector to provide an output corresponding to theconcentrations of the pulp and clay and means responsive to the outputsof the first and second means for I determining the concentration of theclay.

It is advantageous to install a scattered light eliminator behind thesample cell comprising a plurality of parallel light shielding members.1

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings:

FIG. 1 diagrammatically illustrates an embodiment of the novelconcentration measurement apparatus;

FIG. 2 shows a perspective view of one example of a sample cell utilizedin the novel measuring apparatus;

FIG. 3 shows one example of a scattered light eliminator partly brokenaway, utilized in this invention;

FIG. 4 shows a circuit diagram of the measuring apparatus;

FIGS. 5 to 8 show characteristic curves helpful to explain the operationof the novel concentration measuring apparatus;

FIG. 9 is a diagrammatic representation of a modified embodiment of thisinvention; and

FIGS. 10 and 1 1 show characteristic curves to explain the operation ofthe embodiment shown in FIG. 9.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiment of thisinvention shown in FIG. 1 comprises a source of light 1, a filter 2which is used when necessary, a lens 3, and a polarizing element 4, suchas a polarizing plate or a Nicol prism, which can be rotated about itsaxis by an operating knob 41, the angle of rotation being indicated by ascale 42. The liquid to be measured 5, for example, a solutioncontaining an optically active substance such as pulp or sugar iscontained in a cell 6. As shown in FIG. 2, cell 6 comprises a pair oftransparent glass plates 61 and 62 provided with V-shaped grooves 611and 621 on their inner surfaces in the direction of liquid flow, masks63 on the outer surfaces of glass plates to prevent the light fromtransmitting through grooves 611 and 621 and spacers 64 and 65 which areinterposed between glass plates to establish a definite spacingefiective width of the cell) which is determined by the concentration ofthe liquid to be measured. When measuring a solution of lowconcentration pulp (0 1.2 percent), the spacing is about I to 2 mm andit is necessary to decrease the width of the sample cell as theconcentration of the liquid to be measured increases. The sample cell 6includes channel sections 66 defined between parallel V- shaped grooves611 and 621, and effective sections 67 defined between parallel flatsurfaces of the glass plates 61 and 62. Behind the sample cell 6 issituated a seattered light eliminator 7 comprising a plurality ofparallel cylindrical light shielding members 71 which permit lighttransmission only in the axial direction, as shown in FIG. 3. There arealso provided an analyzer 8 comprising a Nicol system orthogonal to thepolarizer, an annular photoelectric detector 9 such as a photocell and acircular disc shaped photoelectric detector 10. Lens 3 is adjusted toilluminate the entire surfaces of photoelectric detectors 9 and 10 bythe light emanated by the source 1.

Turning now to FIG. 4, there is shown a measuring circuit utilized inthis invention. The photoelectric dector 9 is connected in parallel witha fixed resistor R, and a sliding resistor R, which are connected inseries whereas the photoelectric detector 10 is connected in parallelwith a resistor R The sliding arm of the sliding resistor R, and oneterminal of resistor R are connected to the input terminals of anamplifier 11. The output of the amplifier is connected to a reversibleservomotor 12 for driving the sliding arm of the sliding resistor R, asshown by dotted lines.

The novel concentration measuring apparatus operates as follows. Thelight emanated from the source 1 passes through filter 2 and lens 3 andis then converted into linear polarized light by the action of polarizer4 and the polarized light is projected upon the sample cell 6. As abovedescribed, since the sample cell includes grooved sections 66 andeffective sections 67, these two sections manifest different liquidresistances for the flow of the liquid continuously passed through thecell. More particularly, the flow resistance is lower at the groovedsections 66 than at the effective sections 67. For this reason, evenwhen the liquid to be measured contains solid contaminants or lumps,such contaminants and lumps tend to flow through grooved sections 66 atwhich the flow resistance is lower which prevents clogging of theeffective sections 67 by the contaminants and lumps thus assuring astable flow condition. Even when solid contaminants or lumps clog theeffective sections 67 they are quickly removed when they come toapproach the grooved sections 66. It is to be understood that theconfiguration of grooves 611 and 621 is not limited to a V-shape but maybe semicircular, U-shaped or of like configurations. Although groovesare formed on both glass plates, they may be formed on only one of theglass plates. Further, as the grooved sections 66 of the sample cell 6are shielded by masks 63, the presence of such grooved sections does notaffect the result of measurement.

The polarized plane of the light transmitted through the sample cell 6is rotated polarized by the optically active substance such as pulp orsugar contained in the liquid to be measured. Eliminator 7 functions toeliminate the scattered light component from the light transmittedthrough the cell. A portion of the light independent of the opticalactivity is received by the annular photoelectric detector 9 and theremaining portion of the light which is related to the concentration ofthe optically active substance such as the pulp or sugar contained inthe solution is received by the circular disc shaped photoelectricdetector 10.

Output currents from photoelectric detectors 9 and 10 are linearlyrelated to the received light quantity. The relationship between theiroutput currents l and I and the concentration C of the optically activesubstance such as pulp and sugar can be shown by the following equationsof approximation.

1 =I (0) sin (KC) lc 2 where 1 (0): the output current produced by thetransmitted light where C 0,

1 (0): the output current produced by the stray light where theattenuation factor of the transmitted light due to turbidity or coloringof the liquid to be measured,

I the effective length of the sample cell and K, 6,, e constantsdetermined by the configuration of the sample cell, the characteristicof the photoelectric dectors and another factors. FIG. 5 shows therelationship between output current I and I and the concentration C, inwhich FIG. 5A shows the relationship between the concentration of pulpin grams/l. and the output current in microamperes' and FIG. 5B that ofsugar. Output currents I, and I flow through resistors R R, and R andthe difference between voltage drops E and E across these resistors isamplified by amplifier 11 and then applied to the reversible servomotor12 to rotate it in the forward or reverse direction depending upon thepolarity and magnitude of said difference voltage. Rotation of theservomotor 12 moves the sliding arm of the sliding resistor R 13 and thebridge comprised by resistors R R, and R balances automatically when acondition E 1 E is satisfied. Under the balanced condition, followingequation 3 holds:

R=(I, /I )R -R 3 By substituting equation 3 in Equations 1 and 2Equation 4 can be derived out.

Where the optical system is adjusted to satisfy a condition =9, Equation4 becomes as follows sin (KC) R R1 5 Equation 5 shows that the value Rof the sliding resistor R precisely represents the concentration Cwithout being adversely affected by the turbidity or color of the liquidto be measured. Accordingly, it is possible to accurately measure theconcentration of pulp or sugar in the liquid to be measured byindicating or recording the value of the sliding resistor R,, or thedisplacement of its sliding arm or the number of revolution of theservomotor. The resistor R is used for the zero adjustment foreliminating the effect of the stray light 1 (0), whereas resistor R forthe span adjustment.

FIG. 6 shows one example of an experiment, in which FIG. 6A shows theresult of measurement of the concentration of pulp in which case therelationship between concentration C and the deflection of a recordingmeter does not satisfy Equation 5 because of the effect of the scatteredlight caused'by the pulp. In this case, the width of the sample cell was2 mm. FIG.

6B shows the result of measurement of the concenn'ation of sugar inwhich case the relationship between concentration C and the deflectionof the recording meter satisfies Equation 5 because of the absence ofthe effect of the scattered light. In this case, the width of the cellwas 150 mm.

The scattered light eliminator 7 operates as follows. As shown in FIG.3, since the eliminator 7 comprises a plurality of cylindrical lightshielding members 71, transmission of the light crossing the lightshilding members 71 at right angles is perfectly intercepted. When thelight transmitted through the sample cell 6 and containing the diffusedlight component is detected by the photoelectric detector and when itsoutput is detected by an indicating meter, its indication will be benon-linear with regard to the concentration as shown by curve A in FIG.7, whereas the light transmitted through the scattered light eliminator7 is comprised by parallel light beams alone transmitted throughcylindrical light shielding members 71 from which scattered light hasbeen removed, so that an output having a linear characteristic preciselyproportional to the concentration can be obtained as shown by curve B inFIG. 7. The cross-sectional configuration of the light shielding members71 is not limited to circular but may be rectangular or of othersuitable configuration. Instead of providing the diffused lighteliminator 7, the effect of the diffused light can also be eliminated bypositioning the photoelectric detector remote from the sample cell or byvarying the spacing between photoelectric detectors 9 and 10.

In order to always perform correct measurement it is of course necessaryto calibrate the measuring apparatus before its use. In the prior artmeasuring apparatus, it is necessary to prepare a standard liquid of aprescribed concentration, to pour the standard liquid into the samplecell, and to adjust the apparatus until it indicates said prescribedconcentration, Thus, it is very troublesome because it is necessary toprepare the standard liquid whenever the calibration is to be made. Onthe contrary, according to this invention, such calibration can bereadily performed by varying the angle of rotation of the polarizer 4without utilizing the standard liquid. More particularly, when thepolarizer 4 is rotated by knob 41, the indication of the recording meter(the value of the sliding resistor R,) varies with the angle of rotationas shown in FIG. 8. For this reason, by graduating scale 42 in tenns ofthe angle of rotation of the polarizer 4, the apparatus can be readilycalibrated by rotating the polarizer 4 to the desired angle. Suchcalibration can also be made by varying the angle of analyzer 8.

FIG. 9 diagrammatically illustrates a modified embodiment of thisinvention suitable for independently measuring the concentrations of thepulp and clay contained in the stock inlet or whitewater in the papermaking process. The pulp in the stock inlet in a conventional papermaking process generally contains about 0 to 40 percent of clay and thewhitewater also contains pulp and clay. It is thus essential toindependently However, prior art apparatus can not independently measurethe concentrations of pulp and clay. This embodiment comprises acombination of the measuring apparatus shown in FIG. 1 which utilizesthe optical activity of pulp and a concentration measuring apparatus ofthe transmission and scattering type utilizing the scattering of thelight caused by the particles of the pulp and clay. More paricularly,the modified embodiment shown in FIG. 9 comprises a sample cell 21through which is passed a solution 22 such as a stock inlet orwhitewater containing pulp and clay, and a polarized light typeconcentration meter 23 having the same construction as that shown inFIG. 1. Thus, the concentration meter 23 comprises a source of light 31,a lens 32, a polarizer 33, a scattered light eliminator 34 including aplurality of cylindrical or honey comb shaped light shielding members,an annular photoelectric detector 35, an analyzer 36, a circular discshaped photoelectric detector 37 and an operational circuit 38 connectedto receive the outputs from photoelectric detectors 35 and 37. The lightfrom source 31 is adjusted by lens 32 to illuminate the entire surfacesof' photoelectric detectors 35 and 37.

determine the concentrations of both pulp and clay.

There is also provided a transmission and scattering type concentrationmeter 24 comprising a source of light 41, a light shielding plate 42, alens 43, an annular photoelectric detector 44, a circular disc typephotoelectric detector 45 and an operational circuit 46 connected toreceive the outputs from the photoelectric detectors 44 and 45. Thelight from the source 41 is adjusted by the light shielding plate 42 andlens 43 to illuminate only thephotoelectric detector 45. An operationalcircuit 25 is connected to receive the output a of the polarized lighttype concentration meter and the output b of the transmission andscattering type concentration meter. There are also provided anindicating recording meter 26 for indicating and recording the output aof the polarized light type concentration meter 3 and an indicating andrecording meter 27 for indicating and recording the output 0 from theoperating circuit 25.

The operation of the modified embodiment shown in FIG. 9 is as follows:With reference first to the operation of the polarized light typeconcentration meter 23, the light from the source 31 is convertedintoparallel beams by the action of lens 32 and is then linearly polarizedby polarizer 33. The polarized light transmits through the solution 22flowing through sample cell 21. When transmitting through the cell 21,the light is rotated from its polarized plane by the optical activity ofthe pulp contained in the solution. The scattered light component isremoved from the light transmitted through solution 2 by the action ofthe scattered light eliminator 34 and a portion of the transmitted lightfree from the optical activity is projected upon photoelectric detector35 whereas the remaining portion having the optical activity related tothe concentration of the pulp in the solution is received by thephotoelectricdetector 37 The outputs from the photoelectric detectors 35and 37 are directly proportional to their quantities of the receivedlight and their outputs are applied to operational circuit-38 to obtainthe ratio between them. Accordingly, the operational circuit 38 producesthe output a directly proportional -to the concentration of the pulpcontained in solution 22.

This relationship will be discussed in more detail by the aid of FIG.10. Where a solution containing pulp alone is measured by the polarizedlight type concentration meter 23, curve A will be resulted, whereaswhen the solution contains only the clay, curve B will result. As can benoted from these curves, the sensitivity for the clay is lower than forthe pulp. This is because pulp is optically active whereas clay is notactive. This sensitivity for clay is caused by the light scattered bythe clay and such sensitivity can be adjusted by varying the position ofthe photoelectric detector 37 to the left or right as viewed in FIG. 9to vary the angle of incidence of the scattered light. Thus, it ispossible to adjust the output of the solution 22 containing both pulpand clay as measured by the polarized light type concentration meter 23to be within a shaded range C shown in FIG. 10, in which curve A forpulp is included. Thus, with the polarized light type concentrationmeter 23 it is possible to measure the concentration of only the pulp ofthe solution containing both pulp and clay. The output a from thepolarized light type concentration meter 23 is indicated and recorded byindicating recorder 26 and is also applied to operational circuit 25.

Turning now to the transmission and scattering type concentration meter24, the light from light source 41 is converted into parallel lightbeams by lens 43 and the parallel light is then transmitted through thesolution 22 flowing through the sample cell 21 where the light isscattered by the particles of the pulp and clay. A portion of the lightwhich has been scattered in proporation to the concentration is receivedby the photoelectric detector 44 while the remaining portion of thetransmitted light that is independent of the scattering caused byparticles in the solution is received by the photoelectric detector 45.The outputs of these two detectors are also directly proportional to thelight quantities received and their ratio is determined by operationalcircuit 46 which produces output b corresponding to the concentration ofthe sum of pulp and clay in the solution.

This relationship will be discussed further with reference to FIG. 11.When a solution containing the pulp alone is measured by thetransmission and scattering type concentration meter 24, curve A, FIG.11 will be resulted, whereas in the case of a solution containing theclay alone curve B will be obtained. Since the transmission andscattering type concentration meter 24 utilizes the scattering of lightcaused by the particles of pulp and clay the sensitivities for pulp andclay are nearly equal as shown in FIG. 11. Accordingly, where thesolution contains both pulp and clay, the transmission and scatteringtype concentration meter 24 will have an output versus concentrationcharacteristic as shown by curve C, in FIG. 11. When the differencebetween the output a of the polarized light type concentration meter 23and the output b of the transmission and scattering type concentrationmeter 24 is processed by operational circuit 25 it will produce anoutput proportional to the concentration of clay alone, which isindicated and recorded by indicating recorder 27. Thus, theconcentration of the clay in a solution containing both clay and pulpcan be indepently measured.

Although in this embodiment an annular type and circular disc typephotoelectric detectors have been shown the invention is not limited tothese particular type photoelectric detectors. Any detector whichmeasures the concentration of the sample by utilizing the opticalactivity thereof can be used for the polarized light type concentrationmeter and any detector which measures the concentration of the sample byutilizing the scattering of light by the particles of the sample can beused for the transmission and scattering type concentration meter.

Thus, this modified embodiment can independently measure theconcentrations of the clay and pulp contained in the stock inlet orwhitewater in the paper making process. Such independent measurement hasbeen impossible with prior art measuring apparatus.

While the invention has been shown and described in terms of particularembodiments thereof it will be clear that many changes and modificationsmay be made without departing from the true spirit and scope of theinvention as defined in the appended claims.

What is claimed is:

1. Concentration measuring apparatus comprising an orthogonal Nicolsystem including a polarizer and an analyzer, a sample cell disposedbetween said polarizer and said analyzer and adapted to have a liquidsolution containing an optically active substance whose concentration isto be measured flow therethrough, a first photoelectric detectordisposed to receive light which has passed through the polarizer, thesolution and said analyzer for producing an electrical outputrepresentative thereof, a second photoelectric detector disposed toreceive light transmitted only through the polarizer and said solutionfor producing an electrical output representative thereof, and means fordetermining the ratio of the outputs of said first and secondphotoelectric detectors, said sample cell comprising a pair oftransparent plates which are disposed in parallel with spacersinterposed therebetween, at least one of said plates being provided withgrooves on its inner surface extending in the direction of flow of saidliquid, and masks on the outside of said plates for intercepting lightfrom said polarizer directed toward said grooves.

2. The concentration measuring apparatus according to claim 1 whereinsaid first photoelectric detector is in the form of a circular disc andsaid second photoelectric detector is in the form of a circular annulus.

3. The concentration measuring apparatus according to claim 1 wherein ascattered light eliminator is disposed behind said sample cell, and saidscattered light eliminator comprises a plurality of parallel cylindricallight shielding members.

4. The concentration measuring apparatus according to claim 1 whereinsaid polarizer is disposed rotatably and said apparatus is calibrated inresponse to the rotational position of said polarizer.

5. Concentration measuring apparatus for independently measuring theconcentrations of pulp and clay contained in a solution, saidconcentration measuring apparatus comprising: a polarized light typeconcentration meter including an orthogonal Nicol system comprised by apolarizer and an analyzer, a sample cell disposed between said polarizerand said analyzer and adapted to contain said solution, a firstphotoelectric detector disposed to receive light which has passedthrough the polarizer, the solution and said analyzer for producing anelectrical output representative thereof, a second photoelectricdetector disposed to receive light transmitted only through thepolarizer and said solution for producing an electrical outputrepresentative thereof, and first means for determining the ratio of theoutputs of said first and second photoelectric detectors for determiningthe concentration of said pulp in said solution; a transmission andscattering concentration meter including a lens for directing parallellight through i said solution in said sample cell, a third photoelectricdetector disposed to receive said light transmitted by said pulp andsaid clay for producing an electrical output representative thereof, afourth photoelectric detector disposed to receive light scattered bysaid pulp and said clay for producing an electo claim 1 wherein saidanalyzer is disposed rotatably and said apparatus is calibrated inresponse to the rotational position of said analyzer.

i I F

1. Concentration measuring apparatus comprising an orthogonal Nicolsystem including a polarizer and an analyzer, a sample cell disposedbetween said polarizer and said analyzer and adapted to have a liquidsolution containing an optically active substance whose concentration isto be measured flow therethrough, a first photoelectric detectordisposed to receive light which has passed through the polarizer, thesolution and said analyzer for producing an electrical outputrepresentative thereof, a second photoelectric detector disposed toreceive light transmitted only through the polarizer and said solutionfor producing an electrical output representative thereof, and means fordetermining the ratio of the outputs of said first and secondphotoelectric detectors, said sample cell comprising a pair oftransparent plates which are disposed in parallel with spacersinterposed therebetween, at least one of said plates being provided withgrooves on its inner surface extending in the direction of flow of saidliquid, and masks on the outside of said plates for intercepting lightfrom said polarizer directed toward said grooves.
 2. The concentrationmeasuring apparatus according to claim 1 wherein said firstphotoelectric detector is in the form of a circular disc and said secondphotoelectric detector is in the form of a circular annulus.
 3. Theconcentration measuring apparatus according to claim 1 wherein aScattered light eliminator is disposed behind said sample cell, and saidscattered light eliminator comprises a plurality of parallel cylindricallight shielding members.
 4. The concentration measuring apparatusaccording to claim 1 wherein said polarizer is disposed rotatably andsaid apparatus is calibrated in response to the rotational position ofsaid polarizer.
 5. Concentration measuring apparatus for independentlymeasuring the concentrations of pulp and clay contained in a solution,said concentration measuring apparatus comprising: a polarized lighttype concentration meter including an orthogonal Nicol system comprisedby a polarizer and an analyzer, a sample cell disposed between saidpolarizer and said analyzer and adapted to contain said solution, afirst photoelectric detector disposed to receive light which has passedthrough the polarizer, the solution and said analyzer for producing anelectrical output representative thereof, a second photoelectricdetector disposed to receive light transmitted only through thepolarizer and said solution for producing an electrical outputrepresentative thereof, and first means for determining the ratio of theoutputs of said first and second photoelectric detectors for determiningthe concentration of said pulp in said solution; a transmission andscattering concentration meter including a lens for directing parallellight through said solution in said sample cell, a third photoelectricdetector disposed to receive said light transmitted by said pulp andsaid clay for producing an electrical output representative thereof, afourth photoelectric detector disposed to receive light scattered bysaid pulp and said clay for producing an electrical outputrepresentative thereof, and second means responsive to the outputs ofsaid third and fourth photoelectric detectors to provide an outputcorresponding to the concentrations of said pulp and clay; and meansresponsive to the outputs of said first and second means for determiningthe concentration of said clay.
 6. The concentration measuring apparatusaccording to claim 2 wherein said first and second photoelectricdetectors are spaced apart and disposed movably so that the spacingbetween said detectors may be varied.
 7. The concentration measuringapparatus according to claim 1 wherein said analyzer is disposedrotatably and said apparatus is calibrated in response to the rotationalposition of said analyzer.